1. Field of the Invention
The present invention relates to a method of manufacturing a rigid-flexible printed circuit board, and more particularly, to a method of manufacturing a rigid-flexible printed circuit board including a process of providing an anti-oxidation protective layer.
2. Description of the Related Art
In recent times, as the degree of integration of semiconductor elements is gradually increasing, the number of pads provided on the semiconductor elements to connect the semiconductor elements to external circuits is increasing and mounting density is also on an increasing trend. For example, when a minimum processing dimension of the semiconductor element made of silicon is about 0.2 μm, it is required to provide about 1000 pads on the semiconductor element with a size of about 10 mm.
Further, in semiconductor devices such as semiconductor packages, on which the semiconductor elements are mounted, miniaturization and thinning are needed to improve the mounting density, and particularly, in order to respond to portable information devices such as notebook personal computers (PCs), PDAs, and mobile phones, miniaturization and thinning of the semiconductor packages are needed.
In order to package the semiconductor element, it is required to connect the pad of the semiconductor element to a pad of a wiring substrate as well as mounting the semiconductor element on the wiring substrate. However, when about 1000 pads are provided around the semiconductor element with a size of about 10 mm, they are provided with a very fine pitch of about 40 μm. In order to connect the pads provided with a fine pitch to the pad provided on the wiring substrate, since very high accuracy is required for wiring on the wiring substrate or positioning upon connection, it is very difficult to apply a conventional wire bonding or tape automated bonding (TAB) technique.
Accordingly, recently, various multilayer printed circuit boards, which can mount electronic components on surfaces thereof, have been developed according to miniaturization and integration of the electronic components, and particularly, active researches on a flying tail type rigid-flexible printed circuit board, which can minimize a space occupied by a printed circuit board and be three-dimensionally and spatially transformed, are in progress.
This flying tail type rigid-flexible printed circuit board, which consists of a rigid domain (hereinafter, R) having mechanical strength due to an embedded insulating layer and a flexible domain (hereinafter, F) that connects the rigid domains R to each other and has elasticity, is mainly used in small terminals, such as mobile phones, requiring high integration by removing an unnecessary space due to use of a connector in response to demands for high integration and fine pitches of mounted components according to high functionality of mobile devices.
Korean Patent Laid-open Publication No. 10-2010-0081139 (hereinafter, related art document) discloses the invention on a method of manufacturing a rigid-flexible printed circuit board that is capable of minimizing desmear attack occurring when processing a window.
However, when looking into the claim of the related art document, like a conventional typical process of manufacturing a printed circuit board, a rigid-flexible printed circuit board is finally completed through the steps of providing a base substrate divided into a rigid domain R and a flexible domain F, laminating a plurality of circuit layers on the base substrate, and removing the circuit layer in the flexible domain F. In this case, the base substrate may be also damaged by laser light when removing the circuit layer in the flexible domain F. Generally, when laminating a plurality of circuit layers, oxidation (for example, brown or black oxidation) is performed on a surface of the circuit layer, that is, a surface of a metal layer on which a circuit pattern is formed, for improvement of adhesion between the circuit layers. At this time, the metal layer is disclosed by an oxidation solution, and the discolored metal layer absorbs the laser light used for removing the circuit layer in the flexible domain F. In other words, the oxidized metal layer has improved adhesive strength but can't perform a function as a stopper during a laser process due to the discoloration caused by the oxidation. Finally, the laser light is irradiated to the base substrate (flexible film) in the process of removing the circuit layer in the flexible domain F, thus causing damage to the base substrate.
Like this, according to the conventional method of manufacturing a rigid-flexible printed circuit board, the base substrate in the flexible domain F may be damaged, thus eventually causing product defects.